Many types of electronic circuits require a clock signal to operate properly. In many cases, therefore, an integrated circuit (IC) chip includes an oscillator circuit to generate the required clock signal. Some of the common types of oscillator circuits include crystal oscillators, LC (inductor-capacitor) oscillators, RC (resistor-capacitor) oscillators and ring oscillators. Within each type, there are many variations and combinations. However, some advantages and disadvantages or tradeoffs generally apply to the different types.
Crystal oscillators, for example, generally have a very stable frequency, with frequency variations below 100 ppm. However, crystal oscillators require a crystal that is external to the IC chip. The crystal can take up significant board space and add to the cost of the overall electronic device. Additionally, crystal oscillators can have a slow startup time, due to a high Q. (The Q of a crystal oscillator is an indicator of how stable or how wide or narrow band is the frequency response of the crystal oscillator. A crystal oscillator with a high Q, for example, has a very narrow band, so the frequency is very stable.)
LC oscillators generally require a relatively large area for an inductor within the IC chip. Additionally, LC oscillators are generally appropriate for use only in relatively high frequency situations in which a relatively high current (e.g. greater than 100 uA) is available.
RC oscillators and ring oscillators generally require a relatively low area within the IC chip and may be operated with relatively low power levels. However, both types generally suffer from a relatively large frequency variation that depends on variations in manufacturing processes, supply voltage and operating temperature.
It is with respect to these and other background considerations that the present disclosure has evolved.